1. Field of the Invention
This invention relates to a polyester multifilament yarn, particularly to a polyester multifilament yarn which (a) has high modulus and low shrinkage and (b) is useful in the textile reinforcement of tires, providing greatly improved resistance to fatigue and durability on heating, and to a process for producing the polyester multifilament yarn.
2. Description of the Prior Art
Recently it has been demanded that automobiles be superior in comfort, stable in handling during driving at high speed, and light in weight.
Therefore it has been desired to create a yarn having high modulus, low shrinkage, and improved resistance to fatigue and durability on heating as textile reinforcement of the rubber matrix of tires.
A process for producing an improved polyethylene terephthalate multifilament yarn having the above characteristics is disclosed in U.S. Pat. No. 4,101,525. The method disclosed in the above U.S. patent comprises;
(a) extruding a melted polyethylene terephthalate from a spinneret to form a multifilament yarn,
(b) passing the yarn through the solidification zone without heating to cool the yarn immediately,
(c) withdrawing the yarn from the solidification zone under a stress of 0.015 to 0.150 gram per denier, and
(d) drawing the yarn.
This method is superior in obtaining polyethylene terephthalate multifilament yarn which can be used to produce tires having little heat generation during tire rotation when driving.
However, this method has been desired to be improved due to the following problems;
(1) The multifilament yarn can not be stably obtained. The spun yarn tends to break in spinning or in withdrawing, since the yarn is immediately cooled in the solidification zone after spinning. In particular, when a large denier filament yarn is spun, denier unevenness inevitably occurs.
(2) The tenacity of the tire cord which is obtained by twisting the yarn, by spreading an adhesive on the surface of the yarn, and then heat-treating in a stretched condition, decreases in an unusual degree, as compared with the tenacity of the untreated multifilament yarn.
(3) When the tire cord is incorporated in the rubber matrix of tires, decomposition of hydrolysis of the cord is easily caused during the tire rotation when driving.